American Telephone and Telegraph Company; At&t Information Systems

Robert C True

Donald R Means

Noble E Wickliff

A voice-switched telephone circuit with center idle state improves bi-dirional gain control in loudspeaking telephones and thereby enhances the natural quality of interactive conversation. The voice-switched telephone includes: a transmit channel having a microphone and a three-state amplifier; a receiver channel having a three-state amplifier and a loudspeaker; and a hybrid circuit interconnecting the transmit and receive channels to a two-wire telephone line. The present invention is characterized by independent signal level detecting circuits for the transmit and receive channels. When the magnitude of the signal energy in the transmit channel exceeds a predetermined threshold, the transmit channel amplification is increased and the receive channel amplification is decreased by fixed equal amounts. When the magnitude of the signal energy in the receive channel from the two-wire telephone line exceeds a predetermined threshold, the receive channel amplification is increased and the transmit channel amplification is decreased by fixed equal amounts.

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Indianapolis, IN, United States of America

Robert C True